Anticoagulants are substances that prevent coagulation; that is, they stop blood from clotting. Anticoagulants are widely used in human therapy as a medication for thrombotic disorders, for example primary and secondary prevention of deep vein thrombosis, pulmonary embolism, myocardial infarctions and strokes in those who are predisposed.
An important class of oral anticoagulants acts by antagonizing the effects of vitamin K, for example the coumarins which include warfarin. A second class of compounds inhibit coagulation indirectly via a cofactor such as antithrombin III or heparin cofactor II. This includes several low molecular weight heparin products which catalyse the inhibition of predominantly factor Xa (and to a lesser degree thrombin) via antithrombin III (bemiparin, certoparin, dalteparin, enoxaparin, nadroparin, parnaparin, reviparin, tinzaparin), Smaller chain oligosaccharides (fondaparinux, idraparinux) inhibit only factor Xa via antithrombin III. Heparinoids (danaparoid, sulodexide, dermatan sulfate) act via both cofactors and inhibit both factor Xa and thrombin. A third class represents the direct inhibitors of coagulation. Direct factor Xa inhibitors include apixaban, edoxaban, otamixaban, rivaroxaban, and direct thrombin inhibitors include the bivalent hirudins (bivalirudin, lepirudin, desirudin), and the monovalent compounds argatroban and dabigatran.
As blood clotting is a biological mechanism to stop bleeding, a side effect of anticoagulant therapy may be unwanted bleeding events. It is therefore desirable to provide an antidote to be able to stop such anticoagulant-related bleeding events when they occur (Zikria and Ansell, Current Opinion in Hematology 2009, 16(5): 347-356). One way to achieve this is by neutralizing the activity of the anticoagulant compound present in the patient after administration.
Currently available anticoagulant antidotes are protamine (for neutralization of heparin) and vitamin K for neutralization of vitamin K antagonists like warfarin. Fresh frozen plasma and recombinant factor VIIa have also been used as non-specific antidotes in patients under low molecular weight heparin treatment, suffering from major trauma or severe hemorrhage (Lauritzen, B. et al, Blood, 2005, 607A-608A.). Also reported are protamine fragments (U.S. Pat. No. 6,624,141) and small synthetic peptides (U.S. Pat. No. 6,200,955) as heparin or low molecular weight heparin antidotes; and thrombin muteins (U.S. Pat. No. 6,060,300) as antidotes for thrombin inhibitor. Prothrombin intermediates and derivatives have been reported as antidotes to hirudin and synthetic thrombin inhibitors (U.S. Pat. Nos. 5,817,309 and 6,086,871). For direct factor Xa inhibitors, inactive factor Xa analogs have been proposed as antidotes (WO2009042962). Furthermore, recombinant factor VIIa has been used to reverse the effect of indirect antithrombin III dependent factor Xa inhibitors such as fondaparinux and idraparinux (Bijsterveld, N R et al, Circulation, 2002, 106: 2550-2554; Bijsterveld, N R et al, British J. of Haematology, 2004 (124): 653-658). A review of methods of anticoagulant reversal is provided in Schulman and Bijsterveld, Transfusion Medicine Reviews 2007, 21(1): 37-48.
International patent application WO2011089183 discloses antibodies that can bind and neutralize the activity of dabigatran.
There is a need to provide improved antidotes for anticoagulant therapy, and in particular to provide antidotes for direct thrombin inhibitors like dabigatran for which no specific antidotes have been disclosed so far.